Radial flow compressor



Dec. 20, 1960 SCHUG 2,965,287

RADIAL FLOW COMPRESSOR Filed Oct. 18, 1956 INVENTOR Helmui Sc/zu BY M WM2.

ATTORN United States Patent O RADIAL FLOW COMPRESSOR Helmut Schug,Augsburg, Germany, assignor to Maschinenfahrik Augsburg-Nurnberg A.G.,Augsburg, Germany, a corporation of Germany Filed Oct. 18, 1956, Ser.No. 616,847

Claims priority, application Germany Nov. 11, 1955 4 Claims. (Cl.230-134) This invention relates to radial flow compressors and, moreparticularly, to the structure of impeller blades for radial flow gascompressors.

In designing the shape of impeller blades for radial flow compressors itmay be desired to obtain as smooth as possible inlet flow for optimumefiiciency and functioning of the compressor. One may attempt to obtainthis characteristic by forming the impeller blades in a twistedconfiguration radially so that, for each point along the radiallyextending leading edge of the blade, the angle at which the fluid mediumto be compressed enters the blade or impinges thereon corresponds to thedirection of relative velocity resulting from the geometric or vectorialsum of the peripheral velocity and the absolute flow velocity. That is,by the absolute flow velocity is meant here the velocity of a fluidparticle with respect to its surroundings which are at rest, while byrelative velocity is meant the velocity of a moving particle relative toor with respect to the moving impeller blades toward which it isflowing. Also, one may attempt, in developing a radial flow compressorwith inducer blades at the inlet thereof, to form the front part of theblade so that it is bent in a peripheral direction along a line which isinclined to a radial plane in the direction of flow.

Such attempts, however, may require, in order to obtain the desiredinlet angle at the radially inner edge of the blade adjacent the hub,that the inner blade tip be separated from the hub for a portion of itslength. Such undercutting may be quite disadvantageous from thestandpoint of strength since the fatigue strength of such an impellermay be greatly reduced by not having the blades fastened to the rotor orhub completely along the full extent of their inner edges, and the notchformedv in such an arrangement may produce a starting point for cracksor other weaknesses.

If it is attempted to eliminate the undercutting and yet adapt theleading edge of the blade to the different relative velocities atvarious points along the radius of the impeller by providing a bladewith different curvatures along different streamlines, the manufactureand formation of such blades may be quite ditficult and expensive.

According to this invention, however, an impeller blade is provided withthe desired inlet angles and yet with the blade fastened to the rotor orhub of the compressor throughout its entire radially inner edge. This isaccomplished by making the blade so that the surface thereof adjacentthe inlet or leading edge is a portion of the surface of a cylinder theaxis of which lies in a plane parallel to the axis of the impeller andis inclined at an angle to a radial plane in the direction of fiow. Bycorrelation of the angle of inclination of the cylinder axis and itsdistance from the leading edge of the blade and the radius of curvatureof the cylindrical surface according to this invention, blades areprovided having inlet angles corresponding to the directions of therelative velocities at the inlet of the compressor.

One object of this invention is to provide an impeller blade of thecharacter described for a radial flow cornpressor such that the bladehas but a single profile curvature and yet provides an inlet angle whichcorresponds to the direction of relative velocity at various radialpoints along the inlet edge.

Another object of this invention is to provide an impeller blade of thecharacter described having a single cylindrical surface profileconfiguration and also being arranged on the hub or rotor of theimpeller so that the blade is fastened thereto throughout its radiallyinner extent, yet has a leading or inlet edge on which the medium to becompressed impinges with optimum smoothness of flow.

A further object of this invention is to provide a radial flowcompressor of the character described having blades formed as a portionof a cylindrical surface but with leading edges inclined to thedirection of flow to provide inlet flow angles corresponding to thedirection of the relative velocity at various radial points along theleading edge of the blade.

Other objects and advantages will be apparent from the followingdescription, the accompanying drawing,

and the appended claims.

In the drawing Fig. l is a geometric representation of the developmentof the surface of an impeller blade embodying this invention;

Fig. 2 is a partial axial section through a centrifugal compressorembodying this invention;

Fig. 3 is a partial radial section through the impeller of Fig. 2;

Fig. 4 is a section along the line IVIV of Fig. 2; and

Fig. 5 is a section along the line V-V of Fig. 2.

Referring to the drawing, in which like reference characters refer tolike elements throughout the several views thereof, the development ofthe surface of an impeller blade according to this invention isillustrated in Fig. l. The line aa. represents the axis of the impeller,and the plane E is a radial plane perpendicular to E and parallel toaxis a-a. An imaginary cylinder Z is located with its axis zz lying inplane E and inclined to radial plane E, at an angle 5i.e. the anglebetween the cylinder axis zz and the line of intersection d--d of planesE and E The radius of cylinder Z is indicated by r and, in the case ofan infinitely thin blade, would be equal to the distance between plane Eand rotor axis aa. In such a geometric arrangement, the blade itself isformed as a portion of the surface of cylinder Z, and is indicated at Sin Fig. 1 cross-hatched.

Referring to Figs. 2-5, an impeller 1 is indicated for a centrifugalcompressor having axial inlet flow and radial outlet flow. The impeller1 is mounted on a shaft 2.

ing blade portion 3.

Patented Dec. 20, 1960 tion, the various points P P P and P and P areadditionally designated with subscripts 4 and 5 as used in Figs. 4 and5, respectively. Also the designations r and 6 in Figs. 2 and 5 connote,as in Fig. 1, respectively, the radius of curvature of cylinder Z andthe angle of inclination of cylinder axis z-z to radial plane E throughthe impeller. D and D designate, respectively, the diameter of circlesdefined by the radially outer and radially inner extremes of the inletor leading edges 5 of all the blades mounted around the impeller 1.Since the inlet edges 5 are radially or approximately radially disposed,the length of edge 5 is equal or approximately equal to one-half thedifferences between D and D Since the angle P P P is equal to 6, theblade contours of the radially outer and inner blade edges, shown inFig. 4, are arcs of an ellipse with semi-axes a 2 a b the circularfunction r L, tan L,,os (1) For the angle 5 enclosing tangent t, to theellipse are at the radially inner point P there is obtained in a similarmanner L, cos 6 tan B5 Furthermore,

L,,=Li+ -sin6 (3) If the distance L, is selected at least suflicientlylarge so that the angle 5 is smaller than 90, the imaginary cylinder Z,a portion of the surface of which forms the configuration of bladesurface 4, is substantially determined, with its radius and theobliqueness of the inclination of its axis 2-2 to radial plane E by theforegoing functions after the direction of the relative velocity, whichshould correspond to the direction of tangents 1,, and t; are given ordetermined for a particular impeller application.

As noted above, the radial or main blade portion 3 and the more axiallydisposed inducer blade portion 4 can be made integrally of one piece ofmaterial. The ease and economy of manufacture, however, may be enhancedby forming these two portions separately and assembling them together,and in such arrangement the juncture between main blade portion 3 andinducer blade portion 4 lies along the line P --P As will be understood,such juncture is a conical surface developed by rotating the line P -Paround the cylinder axis a-a. Since line P -P is inclined to a radialplane through the impeller at the angle 6, the angle of this conicaljuncture surface is 180 26.

As will be seen from the foregoing, an impeller blade according to thisinvention (or, at least, the inducer portion 4 thereof), has,practically speaking, only a single profile curvature, and that is of acylindrical surface. Accordingly, such a blade surface is quite simpleto manufacture by sheet metal cutting and forming methods, as well as bycasting, forging, or molding. Also, notwithstanding that a bladeembodying this invention may have only a single profile curvature,different inlet angles result at different radial points along theleading edge since, as formed and mounted on the rotor or hub of theimpeller, the cylindrical section actually represents an elliptical arc,

the arc length of which is shorter near the impeller axis.

With the surface of the inducer blade portion 4 developed according tothis invention, the remaining blade surface 3 can be developed in anydesired or conventional manner. Also, since the deflecting of theentering fluid medium to be compressed corresponds to the increase inthe arc length of the elliptical are from radially inner to radiallyouter points, such deflecting occurs over a longer distance at radiallyouter points and higher peripheral speeds than at lower peripheralspeeds. This situation results in substantial efiiciency of compressorshaving inducer blades according to this invention.

While the methods and forms of apparatus herein described constitute apreferred embodiment of the invention, it is to be understood that theinvention is not limited to these precise forms of apparatus, and thatchanges may be made therein without departing from the scope of theinvention which is defined in the appended claims.

I claim:

1. An impeller blade for mounting around the rotor hub of a radial flowcompressor and having an inlet edge, the radially inner end of saidblade being fastened substantially through its entire extent to saidrotor hub, said blade having an inlet surface portion on which flowimpinges upon entering said compressor, said inlet surface portion beinga part of the surface of a cylinder, said cylinder having an axis lyingin a plane parallel to the axis of said compressor and inclined at anangle to a radial plane perpendicular to said compressor axis in thedirection of flow to said blade, and the radius of curvature of saidcylinder and the distance of the axis thereof from said inlet edge ofsaid blade all being cor-. related such that the inlet edge of saidblade terminates in a plane substantially normal to said axis and liesin a substantially radial plane and the inlet angle of said bladecorresponds to the direction of the relative velocities of flowimpinging thereon.

2. An impeller blade for mounting around the rotor hub of a radial flowcompressor and having an inlet edge, the radially inner end of saidblade being fastened substantially through its entire extent to saidrotor hub, said blade having an inlet surface portion on which flowimpinges upon entering said compressor, said inlet surface portion beinga part of the surface of a cylinder, said cylinder having an axis lyingin a plane parallel to the axis of said compressor and being inclined atan angle to a radial plane perpendicular to said compressor axis in thedirection of flow to said blade, said angle and the radius of curvatureof said cylinder being determined by the relations in which L, isdetermined by the relative inlet flow direction at the radially innerextreme of said leading edge, 5,, is the inlet flow angle at theradially outer extreme of said leading edge, 5 is the inlet fiow angleat the radially inner extreme of said leading edge, r is the radius ofsaid cylinder, L, is one-half the chord length of a circular arc endingat the radially outer extreme of said edge D,, is the diameter of thecircle defined by the radially outer extremes of the leading edges ofblades mounted on said rotor, D, is the diameter of the circle definedby the radially inner extremes of the leading edges of blades mounted onsaid rotor, and 6 is the angle of inclination of the axis of saidcylinder to said radial plane.

3 An impeller blade according to claim 2 and having a substantiallyaxially disposed inducer blade portion adjacent the inlet of saidcompressor and a substantially radially disposed main blade portion, thejuncture of said inducer and main blade portions lying on the surface ofa cone the angle of which is 180 minus 26.

4. An impeller blade according to claim 2 and having a substantiallyaxially disposed inducer blade portion adjacent the inlet of saidcompressor and a substantially radially disposed main blade portion inwhich the juncture of said inducer and main blade portions lies on aconical surface having a cone angle of approximately 180 minus twicesaid angle at which said axis of said cylinder is inclined to saidradial plane.

References Cited in the file of this patent UNITED STATES PATENTS GoodOct. 24, 1933 Schubert Dec. 7, 1943 Sollinger Sept. 4, 1945 Campbell etal. May 7, 1946 Millingen et al Mar. 29, 1949 Atkinson Ian. 7, 1958FOREIGN PATENTS Great Britain of 1895

